_____________________________________________________________________________________________________ *Corresponding author: E-mail: kunta.rajesh3@gmail.com; Current Journal of Applied Science and Technology 39(48): 145-152, 2020; Article no.CJAST.64682 ISSN: 2457-1024 (Past name: British Journal of Applied Science & Technology, Past ISSN: 2231-0843, NLM ID: 101664541) Influence of Nitrogen Levels on Physiological Response, Nitrogen Use Efficiency and Yield of Rice (Oryza sativa L.) Genotypes Rajesh Kunta 1* and Ramesh Thatikunta 1 1 Department of Crop Physiology, Professor Jayashankar Telangana State Agricultural University, Hyderabad- 500 030, Telangana, India. Authors’ contributions This work was carried out in collaboration between both authors. Authors RK and RT designed the study, performed the statistical analysis, wrote the protocol, wrote the first draft of the manuscript, managed the analyses of the study and the literature searches. Both authors read and approved the final manuscript. Article Information DOI: 10.9734/CJAST/2020/v39i4831211 Editor(s): (1) Dr. Farjana Sultana, International University of Business Agriculture and Technology (IUBAT University), Bangladesh. Reviewers: (1) Ogie-Odia Efosa. A, Ambrose Alli University, Nigeria. (2) Alaa El-Din Khalil S. Omar, King Faisal University, Kingdom of Saudi Arabia. Complete Peer review History: http://www.sdiarticle4.com/review-history/64682 Received 25 October 2020 Accepted 30 December 2020 Published 31 December 2020 ABSTRACT A field experiment was conducted during 2011-12 to evaluate the efficiency of varying nitrogen fertilizer rates on growth and yield parameters, along with nitrogen use efficiency with two nitrogen levels 60 and 120 kg N ha -1 as main treatments and twenty six rice genotypes as sub treatments. Application of appropriate level of nitrogen fertilization is a major objective to increase nitrogen use efficiency by rice varieties. Among the genotypes, MTU-1001 recorded the maximum grain yield of 5021 kg ha -1 even under application of 60 kg N ha -1 with maximum NUE (Nitrogen Use Efficiency) in 60 kg N ha -1 (83.68) and minimum in 120 kg N ha -1 (45.53). NUE did not increase linearly with the amount of nitrogen application and higher nitrogen levels showed significantly lower NUE values. Maximum yield can be attributed to maximum SCMR (SPAD Chlorophyll meter reading) values, more photosynthetic rate, more tillers and panicles, more number of grains hill -1 , maximum filled grain percentage and minimum spikelet sterility. Original Research Article